Re: [PATCH 05/10] fpu: Make floatx80 invalid encoding settable at runtime

[Richard Henderson <richard.henderson@linaro.org>]

On 2/17/25 04:50, Peter Maydell wrote:
> Because floatx80 has an explicit integer bit, this permits some
> odd encodings where the integer bit is not set correctly for the
> floating point value type. In In Intel terminology the
>   categories are:
>    exp == 0, int = 0, mantissa == 0 : zeroes
>    exp == 0, int = 0, mantissa != 0 : denormals
>    exp == 0, int = 1 : pseudo-denormals
>    0 < exp < 0x7fff, int = 0 : unnormals
>    0 < exp < 0x7fff, int = 1 : normals
>    exp == 0x7fff, int = 0, mantissa == 0 : pseudo-infinities
>    exp == 0x7fff, int = 1, mantissa == 0 : infinities
>    exp == 0x7fff, int = 0, mantissa != 0 : pseudo-NaNs
>    exp == 0x7fff, int = 1, mantissa == 0 : NaNs
> 
> The usual IEEE cases of zero, denormal, normal, inf and NaN are always valid.
> x87 permits as input also pseudo-denormals.
> m68k permits all those and also pseudo-infinities, pseudo-NaNs and unnormals.
> 
> Currently we have an ifdef in floatx80_invalid_encoding() to select
> the x86 vs m68k behaviour.  Add new floatx80_behaviour flags to
> select whether pseudo-NaN and unnormal are valid, and use these
> (plus the existing pseudo_inf_valid flag) to decide whether these
> encodings are invalid at runtime.
> 
> We leave pseudo-denormals as always-valid, since both x86 and m68k
> accept them.
> 
> Signed-off-by: Peter Maydell<peter.maydell@linaro.org>
> ---
>   include/fpu/softfloat-types.h | 14 +++++++
>   include/fpu/softfloat.h       | 70 ++++++++++++++++++-----------------
>   fpu/softfloat.c               |  2 +-
>   target/i386/tcg/fpu_helper.c  | 24 ++++++------
>   target/m68k/cpu.c             | 28 +++++++++++++-
>   5 files changed, 92 insertions(+), 46 deletions(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~